The investigation into 23-year-old Stephen Trudgill’s death comes at a time when the Howard League for Penal Reform has expressed concerns over a rise in self-inflicted deaths and suspected murders in custody.

It said fatalities in British jails were at their highest for 15 years after 199 people died while behind bars, based on Ministry of Justice figures.

Of these four were homicides, with 70 self-inflicted deaths and 103 by natural causes. Twenty-two of the deaths have not been classified as any of the above.

At Highpoint there were two deaths by natural causes and one self-inflicted. However, this did not include Mr Trudgill’s who died on January 9. He was found in his cell just before 9.35pm, according to a police spokeswoman. Mr Trudgill, of Harbord Crescent, Great Yarmouth, was jailed at Norwich Crown Court in December 2008 after admitting 13 arsons, one of which led to more than 100 people being evacuated from their homes.